This problem is quite difficult if you don't remember a technique to solving it.
I will help teach you this tactic.
First, set the percentage over 100, which is 48/100 as a fraction (which is what "over 100" means).
Now, put 12 over x, which is the total amount of students in the class. It should look like this: 12/x.
Now that we've done this, set them up as a proportion.
Your proportion should be:
12/x = 48/100
This is where it becomes a little confusing if you do not remember this correctly.
Cross multiply the denominator (the bottom number of a fraction) of 12/x by the numerator (the top number of a fraction) of 48/100.
This number should be:
48x.
Now, cross multiply the denominator of 48/100 by the numerator of 12/x.
This number should be:
1200.
Our equation now is:
48x = 1200.
To solve for this, divide both sides by 48 to solve for x.
48x / 48 = x
1200 / 48 = 25.
Your equation and solved problem is:
There are 25 total students.
I hope this taught you something and I hope it's very helpful!